Controling boost with the VNT

[quantum]

Well, I have a idea on how to control the VNT to prevent overboost, probably not the cheapest idea, but it seems like it would work. So I thought I would post it up here and see what you guys think.
http://i7.photobucket.com/albums/y252/quantum007/VNTboostmanagement.jpg

Basically, for those of us who don't want to pull apart the motor to put an external wastegate on this may be a "easy" way to get the same result. By putting the external wastegate on the charge pipe you can have it open up at your "overboost" psi; letting the excess pressure exit till the boost becomes under control and then close again when at the correct level. The only problem I can see is that when it opens for how ever long (probably very short time, I'm guessing this will "flutter" to maintain correct boost) till the boost controller can finally take effect; the turbo will loose some of the compressor side pressure which can cause oil to blow by the bearing (I think). What do you guys think?

[quantum]

Anyone going to at least tell me I'm crazy or/and stupid?

Seriously, does this look like it may work? Because if so I may try something like it this winter; but I don't want to waste my time or money it I'm missing something stupid in my design (which is quite likely).

[Aries_Turbo]

i cant imagine how it is going to react but it sounds like what you describe may happen. you will prolly have to set the wastegate on the intake pipe at a higher pressure than the turbo though i would think if you just want to control spikes.

i would actually devise an electronic circuit to so the same thing only a little different.

i designed a circuit a while ago (like over a year) and mpboost and i had a thread about it in the SRT section. you could use that circuit and tap into the map signal wire and the output to a solenoid.
http://www.turbo-mopar.com/forums/photopost/data/522/VNTboostmanagement.gif
ok in the new pic there is no wastegate... you are going to use the bov to do the same task. the solenoid is connected so that the line from the manifold source is normally connected to the bov so that it works like normal.

the vaccum canister is connected so that it maintains a vaccum with the check valve. that is teed into the other input of the solenoid actuating the bov whenever the control circuit is activated.

the control circuit is an adjustable automatic switch that activates whenever it sees a certain voltage from the input.

http://www.turbo-mopar.com/forums/attachment.php?attachmentid=378&d=1138872133

the discussion is in this thread http://www.turbo-mopar.com/forums/showthread.php?t=1193&page=2&highlight=board

so you tap the input into the map sensor wiring and the output to the solenoid. you adjust the setpoint potentiometer so that the desired boost spike level triggers the solenoid and vents through the bov.

you could use a hobbs switch but this will actuate alot faster and have barely any deadzone like the hobbs switch will. plus its cheap to make. :)

Brian

[Aries_Turbo]

oh btw... the price of the circuit is for a 4 stage version... you only need 1 of the items that are labled "4" in the chart.

Brian

[Directconnection]

Anyone going to at least tell me I'm crazy or/and stupid?

Seriously, does this look like it may work? Because if so I may try something like it this winter; but I don't want to waste my time or money it I'm missing something stupid in my design (which is quite likely).

Ever see the Saturday Night Live spoof commercial on Bad Idea Jeans? One guy is telling his pals "I think I'm going to tell my wife about the affair" Then a pic of their butts with the Bad Idea patch. Other guy says something like: "I think it's time I tell my dad that I'm gay. I'm going to spring it on him tomorrow once we're seated at the Bears game." etc.....:D

This one may not have the same consequences, but a bad idea for your turbo. Any time you bleed off the boost at the compressor, the turbo tries to makes up for the difference, right?

[Aries_Turbo]

This one may not have the same consequences, but a bad idea for your turbo. Any time you bleed off the boost at the compressor, the turbo tries to makes up for the difference, right?

not if the control system is really fast and set at a higher point than the wastegate.

the electric system is fast enough that it will open the bov and then as soon as the map volts drop below the setpoint, the solenoid will switch and the diaphram of the bov will now see boost and slam down.

it may flutter a bit till it stays down but i think it should work.

Brian

[Directconnection]

still a band-aid fix. Read the 5digits MOB thread in the SDML archives.

[Aries_Turbo]

link please? i havent the first thought on where to look for that.

Brian

[Directconnection]

It might be on donovan's garage, but it was on the SDML years ago...or was it possibly the FMML which there wouldn't be an archive I think.

I've explained the basics of this before but not in the state of mind to think right now;)

Basically, You want the VANES to be as open and as free flowing as possible, yet still achive maximum boost. Can't control 14psi boost if the minimum attainable boost is 12 or 13psi. Need bigger brakes... make minimum attainable boost lower. 5digits told me to control boost, you need brakes. Set your minimum attainable boost lower.

[Whorse]

There are two lines that go to the VNT actuator. One is for vacuum, one for boost. These are both controlled through solenoids as a part of Chryslers' patented VNT system. If you remove the solenoids you can gain manual control, using restrictors and bleeds. Problem with limiting the boost when it wants more is that we don't have a wastegate, so you are essentially applying back pressure.

The smaller fitting on the actuator is the pressure side. You could try using a pressure regulator and tee-ing a line from the pressure side to the vacuum side that would allow a couple of PSI to the vacuum side, which would keep the vanes in a more closed position. You'd need to mess around to make it work and of course it's not how it was meant to operate, so the wastegate option is recommended.

The design of the VNTs was based around a stock system which used exhaust system backpressure to control it. This was done on purpose because Chrysler couldn't find a feasible way to add a wastegate. Adding a high flowing intercooler and 2.5" cat back exhaust is enough to significantly change the characteristics of how it is controlled. With a stock exhaust and a 944 intercooler, my car overboosts below freezing.

Instead of bleeding boost from the outlet, try bleeding it from the pressure side of the actuator. I would only try this as a temporary fix until adding a wastegate is possible, assuming it actually works (I haven't tried it, but I will once I get my catback installed).

You may also be able to make something work if you bypass the solenoids and control the actuator with lines from the turbo and intake manifold using restrictors.